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Sept. 4, 1956 w. H. wooo ErAL 2,761,332

ROTARY LITHOGRAPHIC PLATE DAMPENING MEANS AND METHOD Filed April 11,1956 2 Sheets-Sheet l [NI/mimics W/u/AM H- W000 BY Hon m0 Sept. 4, 1956w. H. WOOD ETAL 2,761,382

ROTARY LITHOGRAPHIC PLATE DAMPENING MEANS AND METHOD Filed April 11,1956 2 Sheets-Sheet 2 Sat/26E 72 mwzrvrons MLZ/AM 6'- W0 I/owneo 4.PP/TCMRD Arm/vans United States Patent ROTARY LITHOGRAPHIC PLATEDAMPENING MEANS AND METHOD William H. Wood, Mantua, and Howard A.Pritchard, Hiram, Ohio, assignors to Harris-Seybold Company, Cleveland,Ohio, a corporation of Delaware Application April 11, 1956, Serial No.577,503

6 Claims. (Cl. 101-147) This invention relates to a method and apparatusfor applying dampening fluid to lithographic plates or the like formaintaining the non-image areas thereof ink repellent.

For many years the usual dampening system of a lithographic press hascomprised a pair of cloth covered rollers running on the plate, anintermediate or distributing roller contacting the cloth coveredrollers, a slowly turning water feed roller carrying the dampeningfluid, and an oscillating cloth covered ductor roller alternatelycontacting the water feed roller and the intermediate roller. Thissystem has many well recognized disadvantages and much effort has beenspent to improve it or replace it with a different system.

in this connection many arrangements have been devised for applying aspray of dampening fluid directly to the surface of the lithographicplate but none of these arrangements has come into general commercialuse. Two problems in particular are encountered, namely (1) the problemof distributing over the relatively large surface of the plate, infinely divided discrete particles, the extremely small quantity ofdampening fluid which is required by the plate, and (2) the problem ofpreventing contamination of the press and surrounding atmosphere byparticles of dampening fluid which do not reach the plate.

The first of these problems is made difficult by the turbulent conditionof the air close to the surface of the very rapidly traveling plate andby the deflection of the air streams which are ordinarily used to impartvelocity to the spray particles.

Both of these effects result in the more desirable, finer and lighterparticles being carried away by the air currents while those particleswhich do reach the surface are the less desirable larger and heavierones. This results in a tendency to spottiness and a difficulty inapplying very small quantities of dampening fluid.

The second of these problems is diflicult of solution because of thenecessity of providing clearance between the moving surface of the plateand the stationary parts of the dampening device. The air turbulenceadjacent the surface of the rotating plate and the use of air streamsfor imparting velocity to the particles, mentioned above, causesparticles to escape through the clearance space into the surroundingatmosphere. It is essential that such escape be effectively eliminatedsince dampening solutions used in lithography contain, in addition towater, various acids or salts and gums which would corrode orcontaminate the press and would be objectionable to the operator.

In the copending application Serial Number 210,392 of W. H. Wood et al.,filed February 10, 1951, a method of applying dampening fluid directlyto a lithographic plate is described and claimed which in large measureovercomes the problems just referred to.

In addition to past efforts directed toward applying dampening fluid inthe form of a spray directly to the lithographic plate, many deviceshave also been tried, the

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purposes of which have been to (1) apply dampening fluid to the plate byincorporating it in the ink prior to application thereof by the inkingrollers or (2) to improve or eliminate the doctor roller mechanism ofthe usual dampening system.

Referring to the first of these, various ways of incorporating thedampening fluid in the ink have been tried. Among these, the applicationof air-borne particles of dampening fluid to the surface of the inkingrollers in that portion of the inker which is first contacted by thelithographic plate as it rotates, indicates promise and has certainadvantages, for example, freedom from contamination of the fluid supplyby the ink, and preferential localization of emulsification of the ink.

Likewise the use of a spray to dampen the intermediate water roller hascertain advantages in that it eliminates the doctor roll, avoidscontamination of dampening fluid supply by ink picked up by thedampening rollers and conveyed back into the system. and permitscontinuous rather than intermittent application of moisture to thedampening rollers.

While the use of the spray technique for applying dampening fluid to theinking rollers or to the intermediate roller of the usual water systemhas the above stated advantages, some of the same problems exist underthese latter circumstances as exist when one attempts to apply dampeningfluid by spray directly to the lithographic plate. These problems asmentioned above are (1) the difficulty of applying an extremely smallquantity of fluid in particle form uniformly over the surface of thelithographic plate and (2) the difliculty of preventing the escape ofdampening material into the surrounding atmosphere.

The present invention is directed to the solving of these problems inthe situation where it is desired to apply the dampening fluid to theplate through the use of roller means While at the same time employingspray means, with its attendant advantages, for applying the dampeningfluid to the roller means.

Accordingly, objects of the invention, singly and in combination are asfollows:

To provide a dampening method enabling the smooth application of verysmall amounts of dampening fluid over the surface of a lithographicplate.

Enabling such application in a manner which avoids contamination of thedampening fluid supply.

Enabling such application while preventing or minimizing the escape ofdampening fluid into the surrounding air,

Enabling such application to the lithographic plate through roller meanscontacting the plate.

The method of the invention, by which the above objects are achieved,comprises establishing an electrical field of force adjacent a rollermeans which contacts the plate, such field extending the full length ofthe roller means and to a limited extent in a direction transverse tothe length of the roller means, providing finely divided elements ofaqueous dampening fluid suspended in air in the electrical field, whichelements are electrically charged, the field functioning to influencethe particles toward and onto the surface of the roller means, andconveying such deposited particles by the roller means to the surface ofthe plate whereby the non-image areas of the plate are maintained inkrepellent. Different mechanisms for applying the method of the inventionare illustrated in the drawings and pointed out in the claims.

In the drawing,

Fig. 1 is a side view partly in vertical section illustrating anarrangement for depositing fine particles of dampening fluid on rollermeans comprising rollers whose principal function is to convey the fluidto the plate.

Fig. 2 is a similar view illustrating an arrangement wherein fineparticles of dampening fluid are deposited upon certain rollers of aninking mechanism which rollers function to convey both ink and dampeningfluid to the surface of the plate.

Referring to the drawing, represents the plate cylinder of alithographic press of which 11 and 12 are the blanket and impressioncylinders respectively, and 13 is the lithographic plate which is heldin clamps 14 situated in the usual gap 15 of the plate cylinder.

Ink is applied to the lithographic plate 13 by means of form rollers 16,storage rollers 17 and further ink distributing and conveying rollerswhich receive ink from an ink fountain 18 of usual construction andconvey it to the storage rollers, as illustrated.

In the form of the invention illustrated in Figure 1 an electrical fieldof force is established adjacent the rapidly moving surface of rollermeans which run in contact with the lithographic plate 13. This isaccomplished by applying a relative high electrical potential to thewire 19, preferably direct current, and grounding the roller means asindicated at 20. A fog of finely divided particles of dampening fluid iscreated in the chamber 21 and conveyed between the fluid sump 22 and theshield 23 through an opening 24 into the electrical field in the regionadjacent the surface of the roller means. The roller means asillustrated in Fig. 1 comprises a group of three rollers two of whichare numbered 25 and constitute rollers running in contact with the plate13 and a grounded roller 26 in contact with the rollers 25. The rollers25 are cloth covered rollers, termed molleton rollers, and roller 26 isa distributing roller taking the place of the usual intermediate roller.

The fog is preferably generated by opposed nozzles 27 and 28 in thechamber 21 as more fully described in the copending application ofHoward A. Pritchard, Serial No. 278,772, filed March 27, 1952. Such fogis evenly distributed across the width of the machine and travelsthrough the opening between shield 23 and the fluid in sump 22 so that ageneral current of air-borne fog, evenly distributed along the rollermeans 26 is emitted through the opening 24 into the electrical field.The particles of fog are then charged by the ionized atmosphere aroundthe wire 19 and immediately thereafter become influenced by the fieldbetween the wire 19 and the roller 26 and are conveyed by that fieldtoward and onto the surface of the roller 26. These particles are thenconveyed by the action of the rollers 26 and 25 to the surface of theplate 13. The latter is then inked by the rollers 16 in the usualmanner.

In the form of the invention illustrated in Figure 2, use is made ofcertain of the inking rollers of the inking system of the press. In thisform the chamber 21 and the wire 19 and other associated parts arelocated adjacent the first form roller 16 and the first storage roller17 of the inking mechanism which are grounded, these rollers acting toconvey the particles of dampening fluid deposited thereon to the surfaceof the plate 13. While as illustrated the arrangement provides fordeposition of fog particles upon both the rollers 16 and 17, suchdeposition may be limited to either of such rollers but preferablyincludes the first form roller 16. At the extremities of the shell 23there are end plates, indicated at 29, and in the space enclosed by theshell and end plates the fog particles are confined. It will beappreciated however that there is necessarily some space between suchend members and the rollers and also between the shell 23 and therollers. Normally such a condition would permit the escape of relativelylarge amounts of the air-borne fluid particles owing to the turbulenceof the air adjacent the surface of the roller means and owing to the useof air to create the fog and convey it into the region where it is to beused. By the employment of an electrical field of force, however, suchescape is effectively prevented.

It will likewise be appreciated that by the arrangement shown very fineparticles of dampening fluid suspended in air will be utilized. Underordinary circumstances the particles would never reach the surface ofthe roller means owing to the turbulence of air around the rapidlymoving surfaces thereof. Even if such fine particles were given aconsiderable velocity by means of a strong air jet or current, many ofthem, particularly the finest ones, could not reach the surface becausethey would be conveyed away by the air currents deflected away from thesurface of the roller means. By the employment of an electrical fieldacting most strongly upon the finer particles, velocity is imparted tothose particles and they are made to travel toward and attach themselvesto the surface of the roller means by which they may be conveyed then tothe surface of the lithographic plate.

An important feature of the method of this invention lies in theelectrical application of fine fog particles to roller means rather thandirectly to the plate itself. As is well known, plate cylinders,particularly in sheet fed lithographic presses, have a relatively largegap 15 for receiving the ends of the plate. If fine fog particles are tobe deposited directly upon the plate, it is necessary to prevent theirdeposition to as great an extent as possible in the gap of the cylinderfor obvious reasons. It is also necessary to provide some means forminimizing the escape of such particles into the atmosphere which may becaused by the passage of the cylinder gap past the fog applying means.In the method of the present invention, these difficulties are avoidedby electrically depositing the particles upon roller means and conveyingsuch particles to the plate through such roller means. The use of suchroller means eliminates gap problems and the conditions to be met indepositing particles on the rollers are constant throughout each cycleof the press as well as from cycle to cycle as the press continues tooperate.

Thus it will be seen that a method of dampening a lithographic plate hasbeen provided which enables the even application, across the width andthe length of the relatively large surface of a lithographic plate, ofthe extremely small quantity of dampening fluid normally required,without the usually attendant escape of particles into the surroundingair heretofore encountered when utilizing spray methods.

Having thus described our invention, we claim:

1. The method of dampening a lithographic plate mounted upon a rapidlyrotating cylindrical support and contacted by roller means turning atthe same surface speed as said cylindrical support for supplyingdampening fluid and ink to said plate, the ink from said plate beingtransferred to a blanket cylinder and being printed by the lattercylinder on print receiving material by pressure exerted against animpression cylinder, which method comprises establishing an electricalfield of force adjacent said roller means and extending throughout theeffective length thereof and of limited extent in the directiontransverse to the length of said roller means, and providing finelydivided elements of aqueous lithographic plate dampening materialsuspended in air in said field, said elements being electricallycharged, said field being of such potential gradient as to influence themovement of electrically charged particles suspended in air in saidfield toward said roller means while avoiding spark discharge, saidfinely divided electrically charged elements being impelled by saidfield toward said roller means and onto the surface thereof and beingconveyed thereby to the surface of said rotating lithographic plate toapply dampening fluid to adjacent image and non image areas of saidlithographic plate whereby said nonimage areas are maintained in inkrepellent condition.

2. The method as defined in claim 1 wherein said electrical field offorce is adjacent a portion of the roller means which applies ink to theplate.

3. The method as defined in claim 1 wherein said electrical field offorce is located adjacent a surface portion of the roller means whichconveys the finely divided elements of dampening material depositedthereon directly to said lithographic plate without prior contact withany other surface.

4. The method as defined in claim 1 wherein said electrical field offorce is located adjacent a portion of said roller means which isseparated from the portion of said roller means which supplies ink tothe lithographic plate.

5. In mechanism for applying ink repellent material to a plate on theplate cylinder of a rotary lithographic printing machine, a rollparallel to the plate cylinder, means for grounding said roll, means forcreating a fog of aqueous ink repellent material in a narrow fieldadjacent said roll throughout the length thereof, an elongated electrodeparallel to said roll and to the length of 15 said field, and means forapplying a relatively high electrical potential to said electrode,whereby the fine constituents of said fog are impelled toward and ontothe said grounded roll, said mechanism being adapted to to transfer ontothe plate of said plate cylinder the ink repellent material received bysaid grounded roll.

6. Mechanism as defined in claim 5, wherein said grounded roll is thedistributing roller of a dampening mechanism and wherein the inkrepellent material deposited on said distributing roller is transferredby one or more molleton rollers onto the plate of the plate cylinder.

No references cited.

